Advanced Piping Engineering Interview Questions and Answers – Set 2

By: Piping Engineering 

This is the second set in our Piping Engineering Interview Series — covering more advanced and practical-level questions for experienced professionals working in oil & gas, petrochemical, and power industries. Each answer is based on real-world design and stress analysis practices.

🧰 Section 1: Piping Layout & Design Philosophy

1. What are the key factors considered in piping layout design?

Key factors include process requirements, equipment accessibility, maintenance space, stress/flexibility, safety clearances, and minimization of pressure drop. Proper layout ensures constructability and operability.

2. What is the difference between a plot plan and an equipment layout?

A plot plan shows the overall plant arrangement with all equipment and structures. An equipment layout focuses on equipment placement within a unit or area for piping design purposes.

3. How do you decide routing between two pieces of equipment?

Routing depends on shortest practical path, avoiding obstructions, providing thermal expansion flexibility, and meeting process slope or drain/vent requirements.

4. Why are elbows preferred over bends in most cases?

Elbows (standardized fittings) ensure consistency, are readily available, and maintain predictable flow characteristics, while bends are custom-fabricated and used for large-radius or special routing requirements.

5. What is the importance of maintaining slope in certain lines?

Lines carrying condensate, slurry, or gases mixed with liquid require slopes for complete drainage or venting during operation or hydrotesting.

🔩 Section 2: Piping Supports and Restraints

6. What are the main types of piping supports?

• Rest or shoe support (vertical load)
• Guide (restricts lateral movement)
• Line stop (restricts axial movement)
• Anchor (restricts all movements)
• Spring hanger (compensates for vertical displacement)

7. What is the function of a variable spring hanger?

It allows controlled vertical movement under thermal expansion while maintaining nearly constant support load.

8. What is a rigid strut (or snubber)?

Rigid struts resist dynamic loads like wind or seismic but allow thermal expansion. Hydraulic snubbers resist shock loads while allowing slow thermal movement.

9. How do you decide support spacing?

Based on pipe size, material, operating temperature, and span tables from standards like MSS-SP-69. The aim is to limit sagging and bending stress within allowable limits.

10. What are cold supports and hot supports?

Cold supports are designed for installation temperature conditions, while hot supports (like spring hangers) are calibrated for operating (hot) conditions.

🧮 Section 3: Stress Analysis & Caesar II

11. What are the main load combinations in Caesar II analysis?

• Sustained: W + P
• Expansion: (T1 - T2)
• Occasional: W + P + Wind or Seismic
• Hydrotest: W + Test Pressure

12. What are boundary conditions in Caesar II?

Anchors, guides, line stops, and equipment nozzles serve as boundary conditions to simulate real-world restraints on the piping system.

13. How is stress calculated in a pipe bend?

Stress in a bend includes bending stress and ovality effect, adjusted by the bend flexibility factor (k) as per ASME B31.3 equation 319.2.4.

14. What is the allowable displacement stress range?

As per ASME B31.3, S_A = f(1.25Sc + 0.25Sh), where f is the stress range reduction factor depending on the number of cycles.

15. What is the Caesar II restraint summary used for?

To review restraint loads at supports and equipment nozzles to ensure they are within vendor or structural limits.

⚙️ Section 4: Equipment Nozzle Loads & Flexibility

16. How do you handle nozzle load exceedance?

Adjust routing to add flexibility, change support location, introduce expansion joints, or consult the vendor for revised allowable loads.

17. What is WRC 107/297/537?

These are Welding Research Council bulletins that define methods to evaluate local stresses on equipment due to external loads on nozzles.

18. What is the role of an expansion joint?

To absorb thermal movements in restrained systems where routing changes are not feasible. They reduce reaction loads on equipment and supports.

19. What precautions are taken when using bellows?

Proper guides and anchors must be placed near the bellows, as per EJMA standards, to avoid lateral or torsional failure.

20. What is the effect of friction in stress analysis?

Friction resists thermal movement and increases restraint loads, so friction coefficients (typically 0.3 for steel-on-steel) are included in the analysis.

🏭 Section 5: Field & Fabrication Questions

21. What is field weld and shop weld?

Shop welds are done in controlled conditions before site delivery. Field welds are done on-site during erection, often minimized for quality and schedule reasons.

22. What is a pipe shoe and when is it used?

A shoe elevates the pipe from the structure to allow insulation, prevent corrosion, and distribute loads evenly.

23. What is hot tapping?

Connecting a new branch to a live operating line without shutdown, using a tapping machine and isolation valve.

24. What is spool tolerance?

Dimensional tolerance allowed during fabrication to ensure fit-up during erection. Usually ±3mm to ±6mm depending on pipe size.

25. What is field fit-up modification?

Minor adjustment or trimming of pipe spools at site to align mismatched connections due to construction tolerances.

📐 Section 6: Codes, Standards, and Documentation

26. What are the major differences between ASME B31.1 and B31.3 in stress analysis?

B31.1 uses more conservative allowable stresses and simpler equations, whereas B31.3 allows higher flexibility and fatigue-based assessments.

27. What is an MTO (Material Take-Off)?

A document listing all materials required for a piping system — pipes, fittings, valves, gaskets, bolts — used for procurement and cost estimation.

28. What is the purpose of line numbering in a P&ID?

It uniquely identifies a process line and conveys service, size, material, and insulation details for referencing in layout and stress analysis.

29. What is a stress critical line list?

It identifies lines that require detailed stress analysis based on parameters such as size, temperature, pressure, and connection to sensitive equipment.

30. What is the significance of the design temperature?

Highest temperature the piping system can experience under normal operation, used for material selection and stress calculation.

🧠 Section 7: Practical & Troubleshooting Questions

31. How do you identify over-stressed lines?

In Caesar II, check expansion stress (Code Compliance report) — lines exceeding allowable stress range (100%) need routing or support modification.

32. What is an example of a flexibility problem in the field?

When a pipe connected to a pump nozzle causes excessive load due to improper routing or support placement, requiring layout revision or spring addition.

33. What is the role of the stress isometric drawing?

It shows the analyzed routing with nodes, restraints, spring data, and loads. It serves as a reference for fabrication and support installation.

34. What causes misalignment during erection?

Improper fabrication tolerance, thermal expansion not accounted for, or anchor movement. Corrective actions include field adjustment or shimming.

35. How do you handle a line with frequent temperature cycles?

Consider fatigue factors, use flexible routing, and select materials with good fatigue strength. Use ASME B31.3 fatigue curve if required.

📊 Section 8: Advanced Analysis

36. What is modal analysis in Caesar II?

It identifies natural frequencies of the piping system to avoid resonance with external vibration sources like pumps or compressors.

37. What is time history analysis?

Used to study transient loads such as water hammer, relief valve discharge, or seismic time-dependent effects.

38. What is dynamic load factor (DLF)?

A factor applied to convert dynamic loads to equivalent static loads for simplified analysis of impact or vibration cases.

39. How are seismic loads applied in Caesar II?

By specifying seismic coefficients or acceleration spectra as per ASCE 7 or IS 1893 standards, depending on project location.

40. What is the significance of stress intensification factor (SIF)?

It accounts for localized stress increase at fittings (elbows, tees) as per ASME B31.3 Appendix D.